So, overheating not an issue until now, need suggestions!

So the camera overheats, yup, expected, even with the red thermometer warning thing, u can keep shooting for a while before the camera turns itself off.
Well, I'm planning on shooting a 12 hour music festival on one of the hottest days imaginable in Sept.
Not continuously, but on a commissioned basis.
DSLR are you kidding me? you say...
Up until now, my solution for event shooting has been to have multiple 'same model' DSLRs, so when one overheats to the max, I can take it off, set it by a fan, and put another one on while the other one cools off. That - and, the battery grip, which I cannot stress enough, does a wee-bit to keep the camera cooler, as the battery is not directly under the camera during shooting.

My dilemma:
if I have an outdoor vendor set up, with my equipment in the shade, I need a MORE EFFICIENT way to cool down the camera. I've pondered options like multiple fans, A/C machines, etc. My main concern is of course condensation toward the camera.

Any suggestions for "once my 'A' camera overheats, a suitable environment for it to cool down, while I operate my 'B' camera, and continually switch from 'A' to 'B'.... ?